I. Technical Field
The present invention relates to a touch panel having a press detection function which, out of an external force applied to a surface, measures a component in a direction perpendicular to the surface, and a pressure sensitive sensor for the touch panel.
II. Description of the Related Art
Conventionally, a pressure sensitive sensor has been known as a sensor having a press detection function for measuring a pressure of an external force (referred to also as a pressing force) that is applied to a certain surface. As this pressure sensitive sensor, for example, a sensor having a structure described in Japanese Unexamined Patent Publication No. 2002-48658 has been known. The sensor of Patent Document 1 is designed such that plastic films, each formed by stacking an electrode and a pressure sensitive ink layer thereon in this order, are combined with each other so as to make the pressure sensitive ink members face each other, with an insulating layer having adhesive layers disposed on front and rear surfaces being interposed therebetween. Moreover, in the sensor of Japanese Unexamined Patent Publication No. 2002-48658, since concave/convex portions are formed on the front surface of the pressure sensitive ink layer, a space having a predetermined distance is formed between the upper and lower pressure sensitive ink layers so as to prevent the upper and lower pressure sensitive ink layers from being made in tight contact with each other when no pressure is applied thereto.
In the sensor of Japanese Unexamined Patent Publication No. 2002-48658 having the above-mentioned structure, in a case where a pressing force is applied to the upper film, the electrode of the upper film corresponding to the portion pressed by the pressure by the warped upper film is made in contact with the electrode of the lower film through the pressure sensitive ink layer. Thus, the two electrodes are made conductive to each other. In the sensor of Japanese Unexamined Patent Publication No. 2002-48658, by detecting the conductive state of the two electrodes and fluctuations in the resistance value in response to the pressure applied to the pressure sensitive ink layer, it is possible to measure the pressure applied to the upper film. If the sensor of Japanese Unexamined Patent Publication No. 2002-48658 is attached to an inside of a vehicle-use seat, it becomes possible to determine whether or not a passenger is sitting on the seat and also to determine physical characteristics of the passenger based upon a pressure distribution.